Cyclic Heat Flux Research Articles

Advection surface-flux balance controls the seasonal steric sea level amplitude

Along with the mean sea level rise due to climate change, the sea level exhibits natural variations at a large number of different time scales. One of the most important is the one linked with the seasonal cycle. In the Northern Hemisphere winter, the sea level is as much as 20 cm below its summer values in some locations. It is customary to associate these variations with the seasonal cycle of the sea surface net heat flux which drives an upper-ocean thermal expansion creating a positive steric sea level anomaly. Here, using a novel framework based on steric sea level variance budget applied to observations and to the Estimating the Circulation and Climate of the Ocean state estimate, we demonstrate that the steric sea level seasonal cycle amplitude results from a balance between the seasonal sea surface net heat flux and the oceanic advective processes. Moreover, for up to 50% of the ocean surface, surface heat fluxes act to damp the seasonal steric sea level cycle amplitude, which is instead forced by oceanic advection processes. We also show that eddies play an important role in damping the steric sea level seasonal cycle. Our study contributes to a better understanding of the steric sea level mechanisms which is crucial to ensure accurate and reliable climate projections.

High Heat Flux Testing of Brazed W/CuCrZr Monoblock in High Heat Flux Test Facility

The Institute for Plasma Research (IPR) is involved in the development of various technologies for fabrication and testing/qualification of tungsten (W)–based plasma-facing components for ITER-like applications. As a part of these activities, a small-scale W/Cu/CuCrZr monoblock test mock-up is prepared by using a vacuum brazing process. Further, thermal fatigue testing of this test mock-up is performed using the High Heat Flux Test Facility at IPR under an absorbed heat flux of ~9.5 MW/m2 for 1200 thermal cycles. Thermal-hydraulic analysis and computational fluid dynamics (CFD) simulations are also performed to understand the heat flux testing scenario. Nondestructive testing of the test mock-up after thermal cyclic heat flux testing indicates that there are no defects in the test mock-up except for minor cracks on the surface of W tiles. The results of thermal cyclic testing, finite element analysis, CFD analysis, and postanalysis of the High Heat Flux test are presented in the paper.

Cyclic medium heat flux testing of a WTa lattice structure on the HIVE facility

Testing fusion components in high-heat flux conditions is key for assessing the performance of plasma facing components. A novel limiter mock-up design was tested under cyclic thermal loading in the “Heating by Induction to Verify Extremes” (HIVE) facility at UKAEA. The results demonstrated both the capability of the HIVE facility for cyclic thermal loading and the performance of the mock-up limiter.The mock-up comprised a Tungsten-Tantalum additively manufactured lattice brazed to a copper heatsink. Heat fluxes up to 10 MW/m2 were achieved in the testing and a total of 507 pulses were performed with measured heat fluxes of 8 MW/m2 or higher. HIVE diagnostics (IR camera and thermocouples mounted in the sample) found no measurable change in the steady state thermal behaviour of the mock-up. Visual inspection of the sample after testing revealed cracking had occurred in the lattice structure. IR data also revealed that the cracked region of the lattice had a longer cool-down period to the rest of the structure.Preliminary EM analysis to estimate the variation of heat load between a lattice and a solid block was conducted. To gain confidence in such analysis, more computational time as well as thermal and electrical material properties of AM W at temperature are required.

Design, fabrication, and testing of a water-cooled tungsten-foam high-heat flux plasma-facing module

We present a comprehensive study detailing the design, fabrication and testing a new modular “finger” component, featuring a hexagonal tungsten foam armor tile bonded to the top surface of the water-cooled finger unit. The mechanical, thermal, and particle transport properties of the tungsten foam armor were determined for a wide range of porosity and cell size, and then combined in an equivalent solid material with “effective” properties suitable for large-scale simulations. A series of 3-D multiphysics simulations for coupled thermal and mechanical behavior of the “finger” module are used to optimize the design before fabrication. The simulation results show that, for the expected experimental conditions, a safe range of heat flux and foam porosity is possible for both water-cooling and helium-cooling. Based on these multiphysics simulations, an optimum finger cooling module has been fabricated at Ultramet, Inc. A series of experiments were designed to study the thermomechanical performance of the “finger” unit under steady-state and transient thermal loading at surface heat flux up to 16 MW/m2 in the High Energy Flux Test facility (HEFTY) at UCLA. Testing conditions included low-power, steady-state plasma exposure at 6 MW/m2, followed by severe high heat flux cycles at 16 MW/m2. Results of these tests are explained through comparisons with multiphysics simulations. To eliminate the effects of thermomechanical damage carried out on a module on its thermo-mechanical response on a subsequent test, three different yet identically designed and fabricated finger modules were tested. The results show that the current design is capable of cooling the walls of fusion devices at surface heat flux up to 6 MW/m2 without failure, and that the failure heat flux limit is below 16 MW/m2.

Thermo-Mechanical Distortion of Tungsten Coated Steel During High-Heat Flux Testing Using Plasma-Arc Lamps

An experimental setup and a test section were designed and fabricated for high heat flux testing (HHFT) of neutron-irradiated specimens using water-wall plasma-arc lamps. Because of the radiological considerations and limitations of reactor irradiation, the size of the test articles was limited to disks less than 10 mm in diameter. The specimen was clamped onto an actively cooled block, and clamping allowed the insertion of several thermocouples on the back surface of the specimen through a copper (Cu) block. Five vacuum plasma sprayed tungsten (W)–coated F82H steel specimens were subjected to HHFT. Surface profilometry measurements, which were conducted after HHFT, revealed central bowing of the top W surface. This type of residual distortion occurred for all of the specimens, and the larger the specimens were, the larger was the distortion. In an attempt to understand specimen distortion and address the science questions related to the testing of subsize specimens during HHFT, a simplified thermo-mechanical model was developed. By using a measured temperature in the Cu as an isothermal boundary condition, the model eliminated the need for coupling cooling fluid flow models with stress models, greatly simplifying the analysis. The main variable in the proposed model is hC, i.e., the thermal contact conductance between the F82H and the Cu washer. Inelastic properties, including hardening properties, were considered for F82H steel and Cu. Numerical simulation results demonstrated a buildup of residual deformation during HHFT and a very complex state of stress and deformation during typical heat flux (HF) cycling. Hoop stress evolution during a high heat flux cycle reveals that F82H at an interface with W would be mainly in compression during HF application and experienced a transition to a tension state during cooldown. Also, specimen distortion evolves during each HF cycle, as the specimen bows downward during HF application and upward during the cooldown period between HF cycles. The final specimen distortion, i.e., upward bowing of the specimen center, was qualitatively predicted for hC values of 4000 to 5000 W/(m2·K). This hC range of values, for which bulging is obtained, is at the lower spectrum of the range of values for hC, consistent with the low thermal contact conductance expected from the unpolished F82H surface.

Improving the south America wildfires smoke estimates: Integration of polar-orbiting and geostationary satellite fire products in the Brazilian biomass burning emission model (3BEM)

Large land extensions are subjected to environmental degradation and land-use changes by fires annually. In tropical regions, such as South America, the global demand for commodities leads to the conversion of natural vegetation into agricultural land-uses. With the new orbital fire products that have improved in spatial and temporal resolution, it is now possible to better understand fire properties at large scales, such as fire radiative power (FRP), fire spread, heat flux, and fire life cycle. This study aims to integrate polar-orbit and geostationary satellites’ fire-related products to estimate biomass burning (BB) emissions on a continental-scale to better monitor smoke plumes in near-real-time (NRT) while using the Brazilian developments on the Regional Atmospheric Modeling System (BRAMS). The total aerosol optical depth at 550 nm channel from the model during the South American 2020 fire season (September–November) showed a good agreement with Modern-Era Retrospective analysis for Research and Applications (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS) Global Near-Real-Time reanalyzes (R = 0.97, p < 0.05, student t-test). Moreover, the new improvements made in the Brazilian Biomass Burning Emission Model with fire radiative power (3BEM-FRP) better represent smoke emissions of large fire events, such as the Pantanal 2020 fires.

How Well Can Land-Surface Models Represent the Diurnal Cycle of Turbulent Heat Fluxes?

AbstractThe diurnal cycle of solar radiation represents the strongest energetic forcing and dominates the exchange of heat and mass of the land surface with the atmosphere. This diurnal heat redistribution represents a core of land–atmosphere coupling that should be accurately represented in land surface models (LSMs), which are critical parts of weather and climate models. We employ a diagnostic model evaluation approach using a signature-based metric that describes the diurnal variation of heat fluxes. The metric is obtained by decomposing the diurnal variation of surface heat fluxes into their direct response and the phase lag to incoming solar radiation. We employ the output of 13 different LSMs driven with meteorological forcing of 20 FLUXNET sites (PLUMBER dataset). All LSMs show a poor representation of the evaporative fraction and thus the diurnal magnitude of the sensible and latent heat flux under cloud-free conditions. In addition, we find that the diurnal phase of both heat fluxes is poorly represented. The best performing model only reproduces 33% of the evaluated evaporative conditions across the sites. The poor performance of the diurnal cycle of turbulent heat exchange appears to be linked to how models solve for the surface energy balance and redistribute heat into the subsurface. We conclude that a systematic evaluation of diurnal signatures is likely to help to improve the simulated diurnal cycle, better represent land–atmosphere interactions, and therefore improve simulations of the near-surface climate.

Anticyclonic Eddies Enhance the Winter Barrier Layer and Surface Cooling in the Bay of Bengal

AbstractOceanic barrier layer impedes the vertical exchanges of heat and biogeochemical substances between the mixed layer and deep ocean, playing essential roles in modulating air‐sea heat flux and oceanic biogeochemical cycles. Recent studies revealed that mesoscale eddies can modify the vertical motions of the mixed layer. But their influence on the barrier layer has not been determined. By analyzing more than a decade of in situ, satellite, and reanalysis data, this study investigated the influence of eddies on barrier layer in the Bay of Bengal. The results show that the barrier layer in anticyclonic eddies is significantly thickened in winter (by 50% on average). This thickening consists of the deepening of isothermal layer by eddy downwelling and the shoaling of mixed layer by near‐surface salinity restratification. The thickening of the barrier layer enlarges with latitude, in consistent with the reinforcement in salinity stratification and surface cooling. The thickened barrier layer impedes the upward supply of heat into the mixed layer from the below, promoting the winter surface cooling (by 0.7°C on average) and subsurface temperature inversion (by 0.6°C on average). The feature is contrary to the intuitive expectation that anticyclonic eddies possess high sea surface temperature in eddy interiors. As a consequence, both cyclonic and anticyclonic eddies result in negative sea surface temperature anomalies, indicative of a net decrease in the local sea surface temperature. These effects of eddies may be a common feature in salinity‐stratified oceans in winter and have potential implications for the local biogeochemistry and air‐sea coupled models.

Upper-Ocean Eddy Heat Flux across the Antarctic Circumpolar Current in Drake Passage from Observations: Time-Mean and Seasonal Variability

AbstractEddy heat flux plays a fundamental role in the Southern Ocean meridional overturning circulation, providing the only mechanism for poleward heat transport above the topography and below the Ekman layer at the latitudes of Drake Passage. Models and observations identify Drake Passage as one of a handful of hot spots in the Southern Ocean where eddy heat transport across the Antarctic Circumpolar Current (ACC) is enhanced. Quantifying this transport, however, together with its spatial distribution and temporal variability, remains an open question. This study quantifies eddy heat flux as a function of ACC streamlines using a unique 20-yr time series of upper-ocean temperature and velocity transects with unprecedented horizontal resolution. Eddy heat flux is calculated using both time-mean and time-varying streamlines to isolate the dynamically important across-ACC heat flux component. The time-varying streamlines provide the best estimate of the across-ACC component because they track the shifting and meandering of the ACC fronts. The depth-integrated (0–900 m) across-stream eddy heat flux is maximum poleward in the south flank of the Subantarctic Front (−0.10 ± 0.05 GW m−1) and decreases toward the south, becoming statistically insignificant in the Polar Front, indicating heat convergence south of the Subantarctic Front. The time series provides an uncommon opportunity to explore the seasonal cycle of eddy heat flux. Poleward eddy heat flux in the Polar Front Zone is enhanced during austral autumn–winter, suggesting a seasonal variation in eddy-driven upwelling and thus the meridional overturning circulation.

Mean Annual Weather Cycles of some Weather Variables over Warri, Delta State, Nigeria during 2009 to 2018

The importance of analysing the weather cycles of any region cannot be over emphasized considering the dynamic nature of weather and its undesirable impacts on the environment. This study examines the mean annual cyclic behaviour of some weather variables over Warri, Delta State, Nigeria using recent weather data from NiMet for a period of ten years (2009 to 2018). It was observed from the cyclic behaviours from the various weather variables for the ten years period under consideration, that the annual maximum and minimum temperature, vapour pressure and cloud amount cycles follow similar trends, likewise the undulation of the annual soil heat flux cycles. The annual rainfall, wind speed, maximum and minimum relative humidity cycles were found to fluctuate in different patterns. In periods of limited rainfall, relative humidity is at the threshold of ~ 50.0%. A roughly curvilinear fit was noticed between the annual rainfall and relative humidity. While, rainfall appears insensitive to relative humidity changes during the months with lower relative humidity, which tends to be linear during the months with higher relative humidity. Hence, as the rainfall amount increases, there is an increasing tendency towards a curvilinear relationship. The occurrence of the maximum in temperature preceding that of wind speed indicates that the prevalent winds over Warri could be thermally obsessed. The results obtained would assist in providing appropriate panacea to mitigating weather induced environmental hazards, thereby improving agriculture, efficient economic productivity and advance scientific research.

Explaining the Zonal Asymmetry in the Air‐Sea Net Heat Flux Climatology Over the Antarctic Circumpolar Current

AbstractSurface heating occurs over the streamline of the Antarctic Circumpolar Current (ACC) and balances the heat transport associated with the global meridional overturning circulation. With a combination of ocean assimilation model output, objectively analyzed products, and atmospheric reanalysis, this paper investigates the mechanism of climatological surface cooling in the Pacific sector with zonal asymmetry. The poleward shift of the ACC path in the Pacific with barotropic potential vorticity conservation was found to account for this cooling. The southward transport of warm/wet surface waters encounters relatively cold/dry air at high latitudes, causing strong turbulent heat fluxes. Sensible heat flux related to the sea‐air heat convection plays an equivalent role alongside the sea surface evaporative latent heat flux, both of which dominate the surface cooling in the Pacific sector. Solar radiation decreases with a poleward meandering of the ACC, which aggravates the cooling process. A significant seasonal cycle of the ensemble mean net surface heat flux (Qnet) is demonstrated, that is, approximately half‐year heating (cooling) during austral warm (cool) seasons. The estimated magnitude of Qnet over the ACC is approximately 20 W m−2 by averaging 10 heat flux climatologies and 4 W m−2 in an ocean state estimate model. However, efforts are still needed to reduce the excess heat flux over the sea surface in the Southern Ocean for the heat flux products.

Structural and Thermal Analysis of Disc Brake with Slots

The design of braking system of a vehicles is very important in order to minimize the accidents and increase the life span of vehicle, with this motto, in this paper presented the structural analysis, fatigue analysis and thermal analysis of disc brake with slots (DBS) is done by considering various materials of DBS such as carbon alloy, steel and carbon steel. The comparison of those materials is studied in various mechanical and thermal properties such as deformation, strain, stress, factor of safety, number cycles under cyclic loading and heat flux. Simulation studies were done in Ansys 14.5 version. It is observed that the heat flow rate is high in carbon alloy and low in carbon steel material of DBS model. Maximum stress is observed in steel in structural analysis.

Stress analysis of divertor plasma-facing component designs using tungsten particle-reinforced copper composite heat sink

The W-Cu composites are considered as advanced heat sink material for plasma-facing components, depending notably on the reduced macroscopic coefficient of thermal expansion compared with monotonic Cu materials. One class of such W-Cu composite materials is W particle-reinforced Cu composites which can be joined to pure tungsten parts as plasma-facing armor. After heat flux tests with 20 MW/m2 and with a target of 500 cycles, it is found that fracture occurred after around 100 cycles either on the side of W-armor or on the interface between W-armor and W-Cu composite heat sink. In this work, the stress as well as temperature processes during the cyclic heat flux loadings have been investigated with finite-element method for two designs with W-Cu composite materials, and compared with the former design with W-armor and CuCrZr-heat sink. Possible causes for the fracture have been proposed.

Plasma-arc lamp high heat flux cycling exposure of neutron irradiated tungsten materials**This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce

Thick plate, unalloyed W was neutron irradiated in the High Flux Isotope Reactor (HFIR) at 550 °C to a fast fluence of 1.24 × 1025 n m−2 E > 0.1 MeV (∼0.24 dpa). Unirradiated and irradiated specimens of the material were high heat flux (HHF) tested in the Plasma Arc Lamp (PAL) facility. The PAL uses a high-power photon source to provide a broad and even heat distribution on the sample surface. To simulate on/off cycling of normal operating plasma, the samples were exposed to approximately 800 cycles at 4.73 MW m−2 absorbed heat flux (incident heat fluxes of 10.95 MW m−2). After PAL exposure, slight changes were observed on the surfaces of the samples with SEM. The samples showed some annealing in the near surface polished region, but they were all below the damage threshold for cracking or other destructive features. The PAL has a large parameter space for future testing. The use of the HFIR and PAL to sequentially expose neutron irradiated samples to HHF will be a powerful tool for understanding materials behavior in a fusion-like environment.

Creep of stainless steel under heat flux cyclic loading (500-1000C) with different mechanical preloads in a vacuum environment using 3D-DIC

In nuclear fusion reactors, the key structural component (i.e., the plasma-facing component) undergoes high heat flux cyclic loading. To ensure the safety of fusion reactors, an experimental study on the temperature-induced creep of stainless steel under heat flux cyclic loading was performed in the present work. The strains were measured using a stereo digital image correlation technique (3D-DIC). The influence of the heat haze was eliminated, owing to the use of a vacuum environment. The specimen underwent heat flux cycles (500 C-1000 C) with different mechanical preloads (0 kN, 10 kN, 30 kN, and 50 kN). The results revealed that, for a relatively large preload (for example, 50 kN), a single temperature cycle can induce a residual strain of up to 15000.

Study of the Ni–Cr–Fe‐Based Alloy Casting Process using a Mold Simulator Technique

To meet the balance between supply and demand, a Ni–Cr–Fe‐based alloy is tried to be casted using a lab‐scale continuous casting mold simulator. The results show that the temperature of mold wall increases from 73 °C (346 K) maximum to 117 °C (390 K) maximum, whereas the amplitudes of fluctuation of both temperature and heat flux generally reduces, from MF (original Mold Flux) to NF1 (New Mold Flux 1), and then to NF2 (New Mold Flux 2) mold fluxes during the casting process. Ti and Al transfer from molten alloy to mold flux cause the precipitation of high‐melting point CaTiO3 and NaCaAl3(SiO4)3 in mold fluxes, which reduce the infiltration of slags in the gap. In addition, herein, all ten oscillation marks on the alloy shells maintain a strong one‐to‐one correlation with the heat flux cycles. The irregular oscillation marks together with the depression and entrapped slag on the shell mainly result from the uneven heat transfer and slag infiltration.

Diurnal cycle of short-term fluctuations of integrated water vapour above Switzerland

Abstract. The TROpospheric WAter RAdiometer (TROWARA) continuously measures integrated water vapour (IWV) with a time resolution of 6 s at Bern in Switzerland. During summer, we often see that IWV has temporal fluctuations during daytime, while the nighttime data are without fluctuations. The data analysis is focused on the year 2010, where TROWARA has a good data quality without data gaps. We derive the spectrum of the IWV fluctuations in the period range from about 1 to 100 min. The FFT spectrum with a window size of 3 months leads to a serious underestimation of the spectral amplitudes of the fluctuations. Thus, we apply a band pass filtering method to derive the amplitudes as a function of period Tp. The amplitudes are proportional to Tp0.5. Another method is the calculation of the moving standard deviation with time window lengths from about 1 to 100 min. Here, we get similar results to those with the band pass filtering method. At all periods, the IWV fluctuations are strongest during summer, while they are smallest during winter. We derive the diurnal variation of the short-term IWV fluctuations by applying a moving standard deviation with a window length of 10 min. The daily cycle is strongest during the summer season, with standard deviations up to 0.22 mm at about 14:00 CET. The diurnal cycle disappears during wintertime. A similar seasonal behaviour is observed in the diurnal cycle of latent heat flux as provided by the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2 reanalysis) at Bern. Further, the 3 d averages of the latent heat flux and the magnitude of the short-term IWV variability show a strong correlation at Bern in 2010 (r=0.82 with a 95 % confidence interval from 0.75 to 0.87). Thus, we suggest that the diurnal cycle of short-term IWV fluctuations at Bern is mainly caused by large convective heating during daytime in summer.

Seasonal Evolution of the Surface Layer Heat Balance in the Eastern Subtropical Indian Ocean

AbstractThe South Indian Ocean (SIO) is a region of strong air‐sea heat loss due to the unique ocean circulation pattern influenced by the Indonesian Throughflow. In this study, the seasonal variation of the surface layer heat budget in the eastern SIO is investigated using 2 years of measurements from a mooring at 25°S, 100°E, the only colocated upper ocean and surface meteorology time series in the subtropical Indian Ocean. The mooring data are combined with other in situ and satellite data to examine the role of air‐sea fluxes and ocean heat transport on the evolution of mixed layer temperature using heat budget diagnostic models. Results show that on seasonal time scales, mixed layer heat storage in the eastern SIO is mostly balanced by a combination of surface fluxes and turbulent entrainment with a contribution from horizontal advection at times. Solar radiation dominates the seasonal cycle of net surface heat flux, which warms the mixed layer during austral summer (67 W/m2) and cools it during austral winter (−44 W/m2). Entrainment is in good agreement with the heat budget residual for most of the year. Horizontal advection is spatially variable and appears to be dominated by the presence of mesoscale eddies and possibly annual and semiannual Rossby waves propagating from the eastern boundary. Results from the 2‐year mooring‐based data analysis are in reasonably good agreement with a 12‐year regional heat budget analysis around the mooring location using ocean reanalysis products.

Structural and Thermal Analysis of Disc Brake With Drilled Holes Of Various Materials

The design of braking system of a vehicles is very important in order to minimize the accidents and increase the life span of vehicle, with this motto, in this paper presented the structural analysis, fatigue analysis and thermal analysis of disc brake with drilled holes(DBDH) was done by considering various materials of DBDH such as carbon alloy, steel and carbon steel. The comparison of those materials is studied in various mechanical and thermal properties such as deformation, strain, stress, factor of safety, number cycles under cyclic loading and heat flux. Simulation studies were done in Ansys 14.5 version. It is observed that the heat flow rate is high in carbon alloy and low in carbon steel material of DBDH model. Maximum stress is observed in steel in structural analysis.

Using 4-km WRF CONUS simulations to assess impacts of the surface coupling strength on regional climate simulation

Uncertainties in representing land–atmosphere interactions can substantially influence regional climate simulations. Among these uncertainties, the surface exchange coefficient Ch is a critical parameter, controlling the total energy transported from the land surface to the atmosphere. Although it directly impacts the coupling strength between the surface and atmosphere, it has not been properly evaluated for regional climate models. This study assesses the representation of surface coupling strength in a stand-alone Noah-MP land surface model and in coupled 4-km Weather Research and Forecasting (WRF) model simulations. The data collected at eight FLUXNET sites of the Canadian Carbon Program and seven AMRIFLUX sites are used to evaluate the offline Noah-MP simulations. Nine of these FLUXNET sites are used for the evaluation of the coupled WRF simulations. These sites are categorized into three land use types: grassland, cropland, and forest. The surface exchange coefficients derived using three formulations in Noah-MP simulations are compared to those calculated from observations. Then, the default $$ C_{zil} $$ = 0 and new canopy-height dependent $$ C_{zil} $$ are used in coupled WRF simulations over the spring and summer in 2006 to compare their effects on surface heat flux, temperature, and precipitation. When the new canopy-height dependent $$ C_{zil} $$ scheme is used, the simulated Ch exchange coefficient agrees better with observation and improves the daily maximum air temperature and heat flux simulation over grassland and cropland in the US Great Plains. Over grassland, the modeled Ch shows a different diurnal cycle than that for observed Ch, which makes WRF lag behind the observed diurnal cycle of sensible heat flux and temperature. The difference in precipitation between the two schemes is not as clear as the temperature difference because the impact of changing Ch is not local.